ISO 15361:2000: Pulps — Determination of zero-span tensile strength, wet or dry
Tensile strength data at a span length of zero may be used to assess the retention of fibre strength through the entire fibre-processing chain, providing opportunities to optimize fibre characteristics and utilization in various paper grades. Tensile strength values determined at a span length of zero contribute to our understanding of finished sheet strength and are of increasing importance in measuring the impact of new pulping, bleaching and papermaking processes on fibre characteristics.
The zero-span tensile test may be used to determine the strength of pulp fibres when beaten under laboratory conditions, regardless of the laboratory beating procedure used.
Measurement of zero-span tensile strength, in conjunction with tensile strength as well as other physical properties, is useful in optimizing new fibre-processing techniques and maximizing utilization of new fibre sources such as recycled fibres. Papers referenced in the bibliography give further information on the use of zero-span tensile measurements.
The clamping pressure utilized in zero-span testing ensures a maximum clamping effect but cannot totally prevent micro-slippage, whereby the tensile load transmitted in the clamped fibres is dissipated by frictional shear into the clamping jaws.
This micro-slippage means that the ends of some fibres will slip out from beneath the clamping jaw, thereby diminishing the number of fibres carrying the load at tensile failure. In addition, if kinks in fibres are not removed in the beating process, test results may be diminished.
For these reasons, careful interpretation of the zero-span tensile strength value should be exercised in order to separate effects due to the relative number of fibres which are carrying the load at failure, and the effects due to the tensile strength of the individual fibres present in the aggregate.
The zero-span strength values may be different if the samples are tested dry and conditioned, rewetted or wet (never dried).
This International Standard specifies the procedure for determining the tensile strength of laboratory sheets at a test span which is initially zero. It is applicable to all kinds of fibres, including recycled fibres. The laboratory sheets can be tested either dry, rewetted, or never dried.
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply.
However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below.
For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
- ISO 187, Paper, board and pulps — Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples.
- ISO 287, Paper and board — Determination of moisture content — Oven-drying method.
- ISO 536, Paper and board — Determination of grammage.
- ISO 1924-2, Paper and board — Determination of tensile properties — Part 2: Constant rate of elongation method.
- ISO 5263, Pulps — Laboratory wet disintegration.
- ISO 5264-1, Pulps — Laboratory beating — Part 1: Valley beater method.
- ISO 5264-2, Pulps — Laboratory beating — Part 2: PFI mill method.
- ISO 5269-1, Pulps — Preparation of laboratory sheets for physical testing — Part 1: Conventional sheet-former method.
- ISO 5269-2, Pulps — Preparation of laboratory sheets for physical testing — Part 2: Rapid-Köthen method.
- ISO 7213, Pulps — Sampling for testing.
For the purposes of this International Standard, the following terms and definitions apply.
maximum force per unit width that a test piece of the sample will withstand before breaking under the conditions defined in ISO 1924-2
shortest possible span between the clamps that hold the sample; when clamps are adjusted to zero-span, a beam of light aimed between the two clamps is completely interrupted
zero-span tensile strength
tensile strength value measured using an appropriate instrument, with the clamps adjusted to zero-span, under conditions specified in this International Standard
zero-span tensile index
zero-span tensile strength divided by the grammage
Note 1 to entry: Either conditioned or oven-dry grammage may be used in the calculation, and should be reported.